The present invention relates to an evaporated fuel processing device.
An evaporated fuel processing device includes, for example, a fuel tank, a canister for adsorbing evaporated fuel generated in the fuel tank, an atmospheric passage for facilitating communication between the canister and the atmosphere, and a vapor passage for facilitating communication between the fuel tank and the canister. The evaporated fuel processing device further includes an intake pipe for supplying the atmospheric air to an internal combustion engine, a purge passage for communicating the intake pipe with the canister, and a purge pump for forcibly pumping the air from the canister toward the intake pipe. When sufficient negative pressure is generated in the intake pipe, the purge pump is stopped so that the evaporated fuel is desorbed (purged) from inside the canister towards the intake pipe utilizing only the negative pressure in the intake pipe. On the other hand, when sufficient negative pressure is not generated in the intake pipe, the purge pump is driven so that the evaporated fuel is desorbed (purged) from the inside the canister towards the intake pipe.
This type of the evaporated fuel processing device is disclosed, for example, in Japanese-Laid Open Patent Publication No. 2002-256986 and No. 2007-162588. In Japanese-Laid Open Patent Publication No. 2002-256986, a double acting type diaphragm pump is used as a purge pump in order to prevent the fuel vapor from being diffused out of the canister into the atmosphere even when the purge pump is broken. In this way, passage sealing performance can be ensured while the pump is stopped even when the purge pump is broken.
In Japanese-Laid Open Patent Publication No. 2007-162588, a specific vane pump is adopted as a purge pump. The vane pump includes a vane accommodating means, such as a tension spring, which attracts a plurality of vanes to the center of rotation thereof. Therefore, when the purge pump is driven, the centrifugal force causes the tension spring to extend so that the vanes move outwardly in a radial direction to discharge the gas under the pressure. On the other hand, each vane is attracted to the center of rotation due to the biasing force of the tension spring while the purge pump is stopped so that a suction side communicates with the discharge side. As a result, the desorption efficiency of the evaporated fuel is improved since the flow passage of the gas is secured even when the purge pump is stopped. Further, in Japanese-Laid Open Patent Publication No. 2007-162588, the purge pump is provided on the atmospheric passage. However, the gas flowability during oil feeding can be ensured since the flow passage is secured even when the purge pump is stopped.